Hydrogen can be produced from various raw materials such as fossil fuel, biomass, and water. There are growing expectations for hydrogen to be used as an energy source for fuel cell cars and energy for home and business use, for example. Hydrogen is the ultimate clean energy source because only water is left after it is burned. If the use of hydrogen energy as automotive fuel etc. becomes more widespread in the future, it not only can reduce air pollution but also can serve as a fundamental countermeasure against global warming. In order to achieve 80% reduction in carbon dioxide (CO2) emissions by 2050, it is necessary to spread such use of hydrogen energy.
Various studies have been made for hydrogen, and for example, an iridium metal complex is disclosed that causes carbon dioxide to be reduced (hydrogenated) by hydrogen to generate formic acid (see Non-Patent Document 1).